L-asparaginase catalyses the conversion of L-asparagine to L-aspartate. L-asparaginase type II from the bacterium E. coli is a tetrameric high-affinity periplasmic enzyme produced with a cleavable secretion signal sequence. Also known as L-asparagine amidohydrolase, it is the active ingredient in commercially approved drug products indicated for the treatment of patients having acute lymphoblastic leukemia (ALL). For example, Elspar®, approved in the United States for ALL treatment, has as its active ingredient E. coli L-asparaginase type II. Oncaspar® (pegaspargase) contains L-asparaginase (L-asparagine amidohydrolase) that is covalently conjugated to monomethoxypolyethylene glycol (mPEG). Oncaspar is approved in the United States for treatment of first line ALL, as well as ALL and hypersensitivity to native E. coli asparaginase. E. coli L-asparaginase type II is also used to treat other neoplastic conditions. The E. coli asparaginase can be purified from a culture of E. coli to yield the drug substance, e.g., genetically modified E. coli that is deficient in native asparaginase. In some cases, it is expressed from a gene fusion with a heterologous secretion signal peptide.
Periplasmic localization of asparaginase can provide advantages in different expression systems including reduced production of inclusion bodies, reduced proteolysis and generation of an authentic protein N-terminus. Expression yields can be lower due to the limited availability of secretion pathway cofactors and/or the spatial restriction of the periplasmic space. Cytoplasmic expression of recombinant asparaginase, can generate higher yields if the bacterial host cell cytoplasmic environment presents few penalties in regards to solubility, degradation and mis-folding of the asparaginase monomer.